Invasive Species

An invasive non-native species is any non-native organism (plant, animal, fungus or bacterium) that has the ability to spread causing damage to the environment, the economy, our health and the way we live.


Not all non native species are invasive.  Those that are invasive do so through a number of mechanisms and are classified as invasive when their presence has negative impacts on the environment, economy or human health.  A DEFRA commissioned study from 2012 identified 2889 non-native species in the UK of which only 282 were established as invasive non-native species (INNS).    

How did they get here?

INNS have been introduced to the UK either by intentional or unintentional means.  Trade, transport, travel and tourism can all directly link to new biological invasions.  Many species have been introduced  intentionally for commercial purposes such as for agriculture, horticulture, forestry, farming and aquaculture and have escaped and become established in the wild.  Other species have managed to ‘hitch-hike’ on the back of these causing new invasions.         

What’s the problem?

INNS are able to take hold and wreak havoc on newly invaded areas through a number of mechanisms:

The costs associated with INNS are calculated from the impacts they cause and the cost of controlling or eradicating them.  A 2010 DEFRA commissioned report by the Centre for Agricultural Bioscience International (CABI) estimated market costs incurred by INNS to be £1.7 billion per year in the UK and £125 million per year in Wales (now likely to be much higher).  This estimate doesn’t take into account a value for the disturbance of ecosystems services and reducing native biodiversity which is difficult to assess but when considered the total cost of INNS would be much higher.